PHP regex pattern modification needed

Question

I'm sure this has been asked before and I did read through a lot of posts but nothing helped me. Since my regex knowledge is limited I thought I would ask for help.

I need to validate some user input (zip code format). Only certain characters are allowed: A, N, CC, ?, space ( ) and hyphen (-).

Sample Input Data

$input = "CC-XNNNNN", "ANNNNAAA", "AAAA NAA", "ANN ????"

Regex Pattern

$pattern = "(?:C{2})*|A*|N*|\?*|\-*|\ *"

PHP Code

if(preg_match('/' . $pattern . '/', $input))
{
 echo("pass<br>" . PHP_EOL);
}
else
{
 echo("fail<br>" . PHP_EOL);
}

I don't think I need to use anchors, because the allowed characters can be in any position. With the above code I get 'pass' but I should get 'fail' (X not allowed). I've looked this over so much I can't see the forest for the trees anymore.

Can anyone see what I've done wrong? OR is regex the wrong tool for this?

When it comes to regex, I suggest using an online service for testing such as regex101.com. If I put your pattern in there, I get an error message about the |? sequence being invalid — Chris Haas
– Chris Haas, Commented Feb 11, 2021 at 0:38
Do the letters you listed in your question represent something here, like A == alpha, N == numeric, or are these letters literals in your input? — Tangentially Perpendicular
– Tangentially Perpendicular, Commented Feb 11, 2021 at 0:40
@Chris Haas, I did use regex101.com and if I copy/paste my pattern I don't get any error message. But it never fails even when it should. — CharlesEF
– CharlesEF, Commented Feb 11, 2021 at 0:53
@Tangentially Perpendicular, yes they do but that's not what I want tested. I only want the user to enter the allowed valid characters I listed. — CharlesEF
– CharlesEF, Commented Feb 11, 2021 at 0:55
Thanks @CharlesEF, it was a formatting error between markdown and HTML. I made a quick demo of your code and they all appear to pass: 3v4l.org/QpiKQ — Chris Haas
– Chris Haas, Commented Feb 11, 2021 at 2:49

RavinderSingh13 · Accepted Answer · 2021-02-11 00:43:27Z

2

Could you please try following regex, written and tested with shown samples. Online demo of regex is: Regex online demo

^(?:[aA]|[nN]|[cC]{2}|\?|\s+|-)+$

Explanation: Adding detailed explanation for above.

^(?:       ##Starting a non capturing group from starting of value here.
[aA]       ##Checking if its either small a or capital A here.
|[nN]      ##OR if its N or n here.
|[cC]{2}   ##OR its c or C here with 2 occurrences.
|\?        ##Or its ? as a literal character.
|\s+       ##OR its one or more occurrences of spaces.
|-         ##OR its a dash
)+         ##Closing non capturing group and + will make sure only these characters follow
$          ##till end of the value.

Also I have matched characters with their small letter form also in case you don't need that we could change above to: ^(?:A|N|C{2}|\?|\s+|-)+$ then.

answered Feb 11, 2021 at 0:43

RavinderSingh13

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5 Comments

CharlesEF Over a year ago

I've only had time for a small amount of testing. I tried with your pattern (the one with no lowercase). I've found 1 problem with my 4th input sample (ANN ????). Your pattern reports 'fail' when it should be 'pass'. I tried adding *, to allow for zero or many but that didn't work.

RavinderSingh13 Over a year ago

@CharlesEF, I have checked by putting ANNN ???? and it worked fine for me see this once regex101.com/r/ugdAzn/1 let me know how it goes for you, thank you.

CharlesEF Over a year ago

Yes, it appears to work there but it reports 'fail' when I use my PHP code posted above. I will look into it more and report back later. Thanks for the help.

RavinderSingh13 Over a year ago

@CharlesEF, your welcome, cheers and happy learning

CharlesEF Over a year ago

I found the problem. It was the space character. I copy/pasted from Excel into my editor but who knows what happened. In my editor I backspaced and then hit the space bar. Now it passes the test. Thanks again.

The fourth bird · Accepted Answer · 2021-02-11 08:47:03Z

1

You could also use a character class instead of alternating between the single characters.

To also match the lowercase variant, you can use the /i flag

^(?:[AN? -]|CC)+$

The pattern matches:

^ Start of string
(?: Non capture group
- [AN? -] Match one of the listed characters
- | Or
- CC Match CC
)+ Close the group and repeat it 1+ times
$ End of string

Regex demo

edited Feb 11, 2021 at 8:47

answered Feb 11, 2021 at 8:41

The fourth bird

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1 Comment

CharlesEF Over a year ago

Thanks for your solution, it appears to work just as well as RavinderSingh13's answer. He helped me first so he got the credit. Thank you for your input.

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